1. Field
The present disclosure relates generally to composite materials and, in particular, to manufacturing composite parts. Still more particularly, the present disclosure relates to a method and apparatus for forming shapes in layers of composite materials.
2. Background
Aircraft are being designed and manufactured with greater and greater percentages of composite materials. Composite materials may be used in aircraft to decrease the weight of the aircraft. This decreased weight improves performance features such as payload capacities and fuel efficiencies. Further, composite materials provide longer service life for various components in an aircraft.
Composite materials are strong, light-weight materials created by combining two or more functional components. For example, a composite material may include reinforcing fibers bound in a polymer resin matrix. The fibers may be unidirectional or may take the form of a woven cloth or fabric. The fibers and resins are arranged and cured to form a composite material.
Further, using composite materials to create aerospace composite structures potentially allows for portions of an aircraft to be manufactured in larger pieces or sections. For example, a fuselage in an aircraft may be created in cylindrical sections. Other examples include, without limitation, wing sections joined to form a wing or stabilizer sections joined to form a stabilizer.
In manufacturing composite structures, layers of composite material are typically laid up on a tool. The layers of composite material may be comprised of fibers in sheets. These sheets may take the form of fabrics, tape, tows, or other suitable forms. In some cases, resin may be infused or pre-impregnated into the sheets. These types of sheets are commonly referred to as prepreg.
The different layers of prepreg may be laid up in different orientations and different numbers of layers may be used depending on the thickness of the composite structure being manufactured. These layers of prepreg may be laid up by hand or using automated lamination equipment such as a tape laminating machine or a fiber placement system.
A stack of the layers of preform composite material may be placed onto a tool for processing. This stack of composite layers may be referred to as a stack of composite layers and may take the form of a prepreg or preform. The stack of composite layers may be flat and may be placed onto a tool to shape the drape into a desired shape for a composite part.
A layer of flexible material in a flexible sheet may be placed over the stack of composite layers. This flexible material may be an elastomer vacuum bag. A vacuum may then be drawn to apply a vacuum load on the stack of composite layers. When the vacuum is applied, the flexible sheet may be pulled down through the vacuum around the tool to cause the stack of composite layers to change from a substantially flat shape to a desired shape for the composite part.
Oftentimes, the repeated forming of shapes from stacks of composite layers may result in the flexible sheet not performing as desired after a period of time. For example, the flexible sheet may fail while forming a shape from a stack of composite layers. Repeated stress from being stretched over a tool may result in a tear or opening occurring in the flexible sheet. This failure may result in the tool being unavailable for use until the flexible sheet can be replaced with a new flexible sheet.
Therefore, it would be desirable to have a method and apparatus that takes into account at least some of the issues discussed above, as well as other possible issues.